Insight Into the Effect of CuNi(111) and FeNi(111) Surface Structure and Second Metal Composition on Surface Carbon Elimination by O or OH: A Comparison Study with Ni(111) Surface

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A density functional theory (DFT) calculation has been carried out to systematically investigate the mechanism of surface carbon elimination by O and OH on both the alloy FeNi(111) and CuNi(111) surfaces, including the homogeneous and the segregated surfaces, respectively; meanwhile, the obtained results are compared with those on the pure Ni(111) surface in order to probe into the effects of CuNi(111) and FeNi(111) surface structure and second metal composition on the performance of surface carbon elimination. Our results show that compared to the pure Ni(111) surface, the introduction of Fe into Ni increases the adsorption of O, OH, and C species, while it weakens the adsorption of CO and COH; the incorporation of Cu into Ni decreases the adsorption ability of C, O, OH, CO, and COH species. The mechanism of surface carbon elimination by O and OH shows that OH species is more effective for carbon elimination than O species on Ni(111), CuNi(111) surface and the segregated FeNi(111) surface; meanwhile, CuNi(111) and FeNi(111) surface structure and second metal composition have obvious effect on the performance of carbon elimination. Compared to Ni(111), FeNi(111) surface is not favorable for carbon elimination, while CuNi(111) surface is beneficial for carbon elimination, in which the Cu enriched surface is much more favorable than the 1:1 Cu surface and the pure Ni(111), indicating that the segregated CuNi(111) surface with Cu enrichment significantly accelerates carbon elimination. Moreover, the good linear relationship exists between the average adsorption energy of C + O or C + OH and the activation barrier of the C + O(OH) reaction. As a result, once carbon is formed on the segregated CuNi alloy surface with Cu enrichment, carbon deposits can be timely eliminated, which can well explain the reported experimental facts that CuNi bimetallic catalysts with Cu surface enrichment display excellent carbon-resistance ability in CH4/CO2 reforming.